WO2001043492A1

WO2001043492A1 - Pneumatically driven loudspeaker

Info

Publication number: WO2001043492A1
Application number: PCT/SE2000/002191
Authority: WO
Inventors: Arni Ingvarsson
Original assignee: A2 Acoustics Aktiebolag
Priority date: 1999-12-08
Filing date: 2000-11-09
Publication date: 2001-06-14
Also published as: AU2032101A; SE9904465L; SE514782C2; SE9904465D0

Abstract

The invention concerns a pneumatically driven loudspeaker comprising a first chamber (2) having higher pressure than the surroundings (3), where the first chamber has a first opening (6) to the surroundings, and a second chamber (4) having lower pressure than the surroundings (3), where this second chamber has a second opening (9) to the surroundings, whereby the first (6) and the second (9) openings by means of valve mechanisms alternately open and close at a selected frequency, since the valve mechanism consists of at least one flap-like element (5) which with the said frequency swings to and fro, thereby alternately opening and closing both the first opening (6) and the second opening (9).

Description

PNEUMATICALLY DRIVEN LOUDSPEAKER

TECHNICAL FIELD

The invention presented here concerns a pneumatically driven loudspeaker comprising at least one chamber having higher pressure than the surroundings and at least one chamber having lower pressure than the surroundings, as well as an adjustable opening between the respective chambers and the surroundings.

BACKGROUND

Pneumatically driven loudspeakers are previously known. These loudspeakers comprise a chamber with positive pressure, as well as several openings in one wall of the chamber. Over these openings is a slide, which can move in such a way that in one setting it closes the openings and in another setting it opens them. By moving the slide back and forth with a certain frequency, a sound wave of corresponding frequency is obtained by the pulsating emission of compressed air through the openings. Pneumatic loudspeakers have the advantage over other known types of loudspeaker in that they deliver a high output at the same time as they take up relatively little space. This makes them especially suitable for use in, for example, active noise suppression.

A further development of the aforementioned pneumatic loudspeaker is described in patent document PCT/SE99/00586. The loudspeaker in the cited document refers to a pneumatically driven loudspeaker comprising one chamber having higher pressure than the surroundings and one chamber with lower pressure than the surroundings. Each chamber is supplied with at least one adjustable opening to the surroundings, making it possible to alternately open and close the high-pressure and low-pressure chambers to the surroundings by means of a valve mechanism, which means, for example, that the opening to the high-pressure chamber is open while the opening to the low-pressure chamber is closed and vice versa. The frequency at which the modulation of the opening proceeds may be varied. In this way, the efficiency and output of the loudspeaker can be increased. In this context, the term surroundings is understood to mean the environment in which the loudspeaker is operating, which normally means that the surroundings is the air space around the loudspeaker, in which case the surroundings are at atmospheric pressure. Other ambient pressures are naturally possible.

According to the cited document, the air is alternately pressed out from and sucked back into the loudspeaker. This creates a superposition of an exhaust characteristic with an essentially inverted suction characteristic. Both these curves are strongly non-linear, but with the superposition a greater symmetry is achieved in the characteristic. Consequently, the loudspeaker produces a less distorted signal and is therefore easier to control compared to the case where only one chamber with pressure differing from the surroundings is used. The invention is especially suitable for use in active noise suppression because of its high output per weight and area unit, as well as its capacity to operate within a wide range of frequencies.

The described loudspeaker is equipped with a valve mechanism that alternately closes and opens the high-pressure and low-pressure chambers. The described valve mechanism is of a mechanical sort, where the valve mechanism is composed of a reciprocating_slide valve, a rotary valve body, a waddling valve body or a reciprocating valve cone. A common feature of the described valve mechanisms is that they are composed of mechanical components having a relatively large mass, which means that the valve mechanisms have an inherent inertia, which in some applications may mean that they are unable to operate at the required speed. In some applications, it may also be desirable for a loudspeaker to be composed of a large number of interacting loudspeaker cells, in which case the loudspeaker cells are made very small, which is neither simple nor cheap to accomplish using the described mechanical valve mechanisms. The invention presented below illustrates a solution to these problems.

DESCRIPTION OF THE INVENTION

According to an aspect of the invention, it concerns a pneumatically driven loudspeaker comprising at least one chamber having higher pressure than the surroundings and at least one chamber having lower pressure than the surroundings. Subsequently the term chamber is used in the singular, which, however, does not exclude the eventuality that the chamber can be divided into several interacting chambers. Each chamber is supplied with at least one adjustable opening to the surroundings, making it possible to alternately open and close the high-pressure and low-pressure chambers to the surroundings by means of a valve mechanism, which means, for example, that the opening to the high-pressure chamber is open while the opening to the low-pressure chamber is closed and vice versa. The frequency at which the modulation of the opening proceeds may be varied. In accordance with an aspect of the invention, the valve mechanism is comprised of one or more light flaps or wedges, which are made sway to and fro in order to alternately open and close the two chambers, thus allowing a time signal with the desired frequency properties and loudness to be obtained. A flap or wedge is preferably driven by a piezo-electrical actuator, a servo-motor, or micro-actuators, made of, for example, shape memory alloy, bimetal or magnetostriction material.

Additional beneficial features of the invention are evident from the following description and claims. In addition, references in patent document PCT/SE99/00586 to the function and range of application of the loudspeaker also apply.

Throughout the present description, the term chamber is used in the singular to denote a high-pressure or low-pressure chamber in the loudspeaker. This, however, does not exclude the possibility that either of the chambers may be divided into several interacting sub-chambers.

An advantage of the invention in accordance with the aspect of the invention is that a loudspeaker is obtained which is very easy to control and that it can very quickly follow a wide-band time signal, since the movable parts have very low inertia. An additional advantage is that it is easy to miniaturize the loudspeaker cells, i.e. make them light and compact. The loudspeaker cells may, for example, be made using MEMS technology, which permits the making of a large number of loudspeaker cells in a given area, thereby acquiring a wide-band sound source that, with several small loudspeaker cells distributed on an area, also provides scope for controlling the lobe form of the sound from the sound source produced by the interacting cells. DESCRIPTION OF DRAWINGS

Fig. 1 shows a schematic sectional view through a loudspeaker in accordance with an aspect of the invention, in which a piezo-electrically controlled plate opens and closes the opening to a high-pressure and low-pressure chamber in the loudspeaker.

Fig. 2 illustrates, in a corresponding way, two pliable plates, which interact on opening and closing of both the high-pressure and low-pressure chambers.

DESCRIPTION OF EMBODIMENTS

A number of embodiments of the invention are described below with the aid of the attached drawings.

A section of a loudspeaker 1 in accordance with the invention is reproduced in Fig. 1. The drawing shows that the loudspeaker 1 comprises a first chamber 2 having higher pressure P+ than the surroundings 3, where the pressure in this embodiment is atmospheric pressure P. A second chamber 4 in the loudspeaker has a lower pressure P- than the surroundings. The first chamber 2 and the second chamber 4 are separated by a partition wall 5. A first opening 6 is arranged between the first chamber 2 and the surroundings 3 between the partition wall 5 and the wall 7 of the first chamber. The wall 7 of the first chamber is preferably terminated by a first lip 8. In the same way, a second opening 9 is arranged between the second chamber 4 and the surroundings 3 between the partition wall 5 and the wall of the second chamber 10. The wall 7 of the second chamber is preferably terminated with a second lip 11. The first lip 8 and the second lip 11 in this embodiment define an opening to the surroundings 3 common to both the first and second chambers. This common mouth is symmetrically positioned in relation to the partition wall 5, which is terminated at a defined distance from the said mouth.

A piezo-electric plate acts as a flap 12, one end of which is attached to the termination of the partition wall 5. The other end of the flap may be bent towards either the first lip 8 or the second lip 11. When the flap 12 is bent towards the first lip 8, the first opening 6 closes, whereby the first chamber 2 with pressure P+ closes to the surroundings 3. With the flap 12 in this position, the second chamber 4 having pressure P- is open to the surroundings, which means that air will flow into the second chamber. When the flap 12 is bent towards the second lip 1 1, the second opening 9 closes, whereby the second chamber 4 with pressure P- closes to the surroundings 3. With the flap 12 in this position, the first chamber 2 having pressure P+ is open to the surroundings, which means that air will flow out from the first chamber. Since the flap 12 is comprised of a piezo-electric plate, it can be made to oscillate to and fro with the desired frequency, thereby generating a very strong sound at the opening 3 to the surroundings, a result of the great variations in pressure which occur there, when air flows into the low-pressure chamber 4 and flows out of the high-pressure chamber 2.

Fig. 2 shows an alternative embodiment, in which the mechanical structure of the loudspeaker is unchanged, the only difference being, that two pliable flaps 13, 14 of piezo-electric material are used. A first flap 13 is attached at one end to the first lip 8, while the other end of the first flap 13 can be bent towards the termination of the partition wall 5, so that in this setting the first chamber 2 is closed. A second flap 14 is attached at one end to the second lip 11 and is bent away from the termination of the partition wall 5, so that in this setting the second chamber 4 is closed, which implies that air will flow out of the low-pressure chamber 4. The first and second flap can be controlled by the same pressure and synchronised with the same frequency, so that they oscillate back and forth in phase with one another. It is also possible to control each flap individually in order to compensate for non-symmetry in airflow out of and into both of the chambers 2, 4.

Since it is possible to design both of the pressure chambers 2, 4 as small as is mechanically feasible, and to make the dirigible flap 12, 13, 14 the corresponding size, a loudspeaker cell can be made very small, for example smaller than the acoustic wavelength, which implies a size in the order of a few millimetres. This implies that it is possible to construct a loudspeaker that is in turn made of a large number of loudspeaker cells 1 in accordance with the invention, where the individual loudspeaker cells can be distributed over a greater area according to a desired pattern, thus giving the loudspeaker with its interacting loudspeaker cells the desired directivity. The position of the individual loudspeaker cells and their individual design can also be modelled in order to obtain the desired directivity and/or sound character. It is even possible to integrate such small loudspeaker cells with electronics in circuits by constructing the loudspeaker using MEMS technology (Microelectromechanical Structures). The individual loudspeaker cells can be made interact with each other to produce greater acoustic power, and/or can be controlled individually to give the overall sound the desired character.

Claims

1. Pneumatically driven loudspeaker comprising: a) at least a first chamber (2) having higher pressure than the surroundings (3), where the first chamber has at least one first opening (6) to the surroundings, b) at least a second chamber (4) with lower pressure than the surroundings (3), where this second chamber has at least one second opening (9) to the surroundings, and that the first (6) and the second (9) openings by means of valve mechanisms alternately open and close at a selected frequency, characterised in that a valve mechanism consists of at least one flap-like element (5) which with the said frequency swings to and fro, thereby opening and closing both the first opening (6) and the second opening (9).

2. A loudspeaker as in claim 1 , characterised in that the wall (7) of the first chamber (2) and the wall (10) of the second chamber (4) form an opening to the surroundings (3) that is common to both chambers (2, 4).

3. A loudspeaker as in claim 2, characterised in that the flap element (5) is connected at one end to a wall which separates the first chamber (2) from the second chamber (4), and that the other end of the flap element is made, while oscillating, lie alternately against the end of the first wall (8) so as to close the first opening (6) and against the end of the second wall (11) so as to close the second opening (9).

4. A loudspeaker as in claim 2, characterised in that one end of a first flap element (13) is connected to the end (8) of the first wall (7), while its other end is able to oscillate to and fro so as to, in one position of oscillation, close the first chamber (2), and that a second flap element (14) is connected to the end

(1 1) of the second wall (10), and is able with its other end to oscillate to and fro so as to, in one position of oscillation, close the second chamber (4).

5. A loudspeaker as in any of the preceding claims, characterised in that the oscillating flap (5, 13, 14) is, partly at least, embodied by a piezo-electric element.

6. A loudspeaker as in any of the claims 1 to 4, characterised in that the oscillating flap (5, 13, 14) is, partly at least, embodied by one of the following materials: shape memory alloy, bimetal or magnetostriction material.

7. A loudspeaker as in any of the claims 1 to 4, characterised in that the oscillating flap (5, 13, 14) is driven by an actuator, for example a piezo-electric element.

8. A loudspeaker as in claim 1, characterised in that the loudspeaker is made by MEMS technology.

9. A loudspeaker as in claim 8, characterised in that the loudspeaker is made by MEMS technology and electronically integrated on a printed circuit card.

10. Use of a loudspeaker according to claim 1 or 9, characterised in that several loudspeakers are built together over a surface and wherein each individual loudspeaker (1) is contrilled in order to cooperate with the rest of the loudspeakers (1) in order to obtain at least one of the features: a) higher sound effect, b) desired directing result, c) desired sound characteristics.